A television receiver requires separating a color signal and a luminance signal from a composite video signal. A simple method for separating the signals is, for example, a method with using a band pass filter (i.e., BPF) or a method with using a comb filter.
The method with using a BPF is described as follows. A composite video signal is input into the BPF. The color signal desired is an output signal of the BPF. The luminance signal desired is the subtraction result of the predetermined color signal from the composite video signal. Here the BPF has the ability that the BPF passes only a signal component within a color-signal-band. The method using a comb filter is described as follows. The luminance signal desired is the addition result between a one-line-delayed composite video signal and a non-delayed composite video signal. The color signal desired is the subtraction result of the one-line delayed composite-video-signal from the non-delayed composite video signal. Here, the separation is executed using the information on a phase correlation between the lines.
The two methods mentioned above are easy to perform but result in quality losses of videos such as that due to cross color and dot interference.
An addition of a field memory and a complicated circuit on a display is a method for improving the video quality loss. An example is shown in JP-A-H09-163398, in which the following technique is presented. Output signals of the field delay circuit and the line delay circuit are input into filters. Then output signals of these filters are to be desired signals by selecting the output signals. The selection of the output signals is made based on the decorrelation-detection-result obtained by limiting a band in relation to time, vertical, and horizontal components.
An application of a complicated circuit is shown in JP-A-H09-163398 to a small display such as a vehicle display and a mobile display, however, leads to display devices having a much bigger sized circuit than its screen size. Moreover, some information losses of a video signal may not be relevant to an actual video quality for audiences in use in taking into account the screen area of the display. An application of the large circuit exampled in JP-A-H09-163398 to the small display provides an overmuch resolution in use. The small display having a complicated circuit is shown in JP-A-H09-163398 poses problems of a non-suitable sized circuit for the display and the overmuch resolution in use. Thus, what is required is a signal separator without having a large circuit. Further, it is required for the signal separator to provide an appropriate video quality with reducing quality loss such as that due to cross color and dot interference.